Abstract: Suspended particulate and fecal coliform bacteria concentrations measured in the
riparian swamps of two differing tidal river systems, one brownwater and one blackwater,
in southeast North Carolina indicate that both swamp surfaces export fecal coliform
bacteria to the river. The measurements of suspended particulates and fecal coliforms
spanned a six-month period and were carried out to determine the extent to which these
systems serve as sinks for the coliform bacteria, and to relate the changes in bacterial
concentrations during inundation events to the availability of suspended particulates in
each of the river systems. Results of this study suggest that in both types of swamps, the
fecal coliform bacteria were not associated with suspended particles, and that the swamp
surface was a source of bacteria ultimately exported to the river during an inundation
event. Temporal variations in bacteria concentrations, results from replicate sampling
that examined differences in coliform concentration between rising and falling water, and
several anecdotal observations further suggest that the swamp surface is a source of
bacteria, as opposed to a sink. To explain the export of bacteria from the swamp surface,
a conceptual model was developed based upon the changes in fecal coliform
concentration, flow patterns on the swamp surface, and the relative contribution of river
water and swamp water. Higher concentrations of bacteria were present in the water
during falling water phase because additional bacteria are picked up from the sediment
and debris on the surface as long as the water is in contact with the swamp surface. Thus,
waters having had greater contact with the swamp surface, contained higher
concentrations of bacteria. Because this study was conducted during a time when the
watershed, particularly the brownwater system, was affected by a severe drought, the results were different from those originally anticipated. The reduced streamflow in the
mainstem river lowered the availability of fecal coliform bacteria and TSS to the swamp
surface, which may explain why the brownwater swamp surface exported bacteria instead
of trapping the bacteria. The results of this study suggest that the swamp surfaces may
always have an export of bacteria, but that during normal streamflow conditions
(particularly in the brownwater) this export of bacteria may be undetectable due to
increased concentrations of larger-grained suspended particulates.